AhmadNadiy Bin Mohd Ghazali Dissertation submitted in partial … · 2020. 5. 7. · TRONOH, PERAK January2009. CERTIFICATION OF ORIGINALITY This is to certify that I am responsible

Development of a Computer Programto Assess Gas Compressor Performance

by

Ahmad Nadiy Bin Mohd Ghazali

Dissertation submitted in partial fulfillment of

the requirements for the

Bachelor of Engineering (Hons)

(Mechanical Engineering)

JANUARY 2009

Universiti Teknologi PETRONASBandar Seri Iskandar

31750 Tronoh

Perak Darul Ridzuan

2G=f. S"

9 Cdt^^r-eSSoY^- • lesii^A.

5) Ub --ikes^r

Approved by,

(Ir. Idris

CERTIFICATION OF APPROVAL

Development of a Computer Program to AssessGas Compressor Performance

by

Ahmad Nadiy B Mohd Ghazali

A project dissertation submitted to the

Mechanical Engineering Programme

Universiti Teknologi PETRONAS

in partial fulfilment of the requirement for the

BACHELOR OF ENGINEERING (Hons)

(MECHANICAL ENGINEERING)

Wnabin Ibrahim, P.Eng. MIEMSenior LecturerMecfianical Engineering DepartmentUniversiti Teknotogi PETRONAS

UNIVERSITI TEKNOLOGI PETRONAS

TRONOH, PERAK

January 2009

CERTIFICATION OF ORIGINALITY

This is to certify that I am responsible for the work submitted in this project, that the

original work is my own except as specified in the referenced and acknowledgements,

and that the original work contained herein have not been undertaken or done by

unspecified sources or persons.

(AHMAD NADIY B MOHD GHAZALI)

11

ABSTRACT

This report discusses the preliminary research done and basic understanding of the

chosen topic, which is Development of a Computer Program to Assess Gas Compressor

Performance. The author has compiled all the materials related to the topic and utilizes

them as the main source to start the project. The main objective of the project is to

develop a computer program for the usage of evaluating the performance of gas

compressor specifically centrifugal compressor performance. There are two (2) phases in

the development of the computer program. The first phase is the development ofthe basic

spreadsheet which has a very limited function but stillable to perform the calculations to

assess gas compressor performance. The second phase is the critical improvement of the

program which more user-friendly and has modern-look. This project enhanced the

assessment of gas compressor performance by eliminating the usage of manual

calculations on a basic spreadsheet to evaluate the gas compressor performance. Byusingthis computer program, gas compressor operators will be able to perform calculations bygiving inputs to this program and get specific outputs in order for them to use for

assessment. The outputs of this program which are in a graph plots can be assessed to

evaluate the performance of the gas compressor. Recommendations were given to

improve the design and features of the computer program foranyfutureworks.

in

ACKNOWLEDGEMENT

This thesis is submitted in fulfillment of the requirements for the degree in Mechanical

Engineering at the University Technology PETRONAS, Malaysia. The research

presented has been carried out at the University Technology PETRONAS in the period

from July 2008 to June 2009.

I would like to use this opportunity to thank my supervisor at University Technology

PETRONAS, Ir. Haji Idris Ibrahim for the guidance,help and critique during this work.

I would also like to thank the PETRONAS Bintulu Fertilizer, Sarawak specifically En.

Mohd Izhar Mohd Ghazali for providing me with the necessary data and information that

contributes to the development of this project. I am grateful his cooperation in order to

make this project a success.

Not forgetting my previous plant supervisors, En. Nurhisyam and En. Restoto from

PETRONAS Carigali Sdn Bhd (PCSB), KLCC which had given me guidance in

understanding the necessary knowledge and information that allow me to carry out this

project.

Finally, I would like to thank my colleague, En. Muamar Gadafi for his supports

throughout the completion of this work.

IV

TABLE OF CONTENTS

CERTIFICATION h"

ABSTRACT iii

ACKNOWLEDGEMENT iv

LIST OF FIGURES vi

LIST OF TABLES vii

CHAPTER 1: INTRODUCTION 1

1.1 BACKGROUND OF STUDY 1

1.2 PROBLEM STATEMENT 6

1.3 OBJECTIVES 6

1.4 SCOPE OF STUDY 6

CHAPTER 2: LITERATURE REVIEW 6

2.5 LITERATURE REVIEW 7

CHAPTER 3: METHODOLOGY 13

3.1 METHODOLOGY AND PROJECT WORK 13

CHAPTER 4: RESULTS 18

4.1 THE PLANT DATA 18

4.2 THE PERFORMANCE CURVE 23

4.3 COMPRESSOR EFFICIENCY VS FLOWRATE 24

CHAPTER 5: DATA EVALUATION & DISCUSSION 26

5.1 DATA EVALUATION 26

CONCLUSION 31

RECOMMENDATIONS 32

REFERENCES 33

APPENDICES vi

LIST OF FIGURES

Figure 1.1 Basic principles of centrifugal compressor 1

Figure 1.2 Compression ofhigh velocity gas through the diffuser 2

Figure 1.3 Stage of Compression 3

Figure 1.4 Compressor performance curve (optimum design point) 4

Figure 1.5 Overall picture of Centrifugal Compressor Assessment 5

Figure 2.1 Compressor Performance Curve 8

Figure 2.2 Anyprocess changes willmoves the operating point on the curve 11

Figure 3.1 Methodology of the entire project 21

Figure 4.1 Performance Curve of the Design Point 23

Figure 4.2 Performance Curve of the Actual OperationData 24

Figure 4.3 Compressore Efficiency vs Flowrate (Design Popint) 25

Figure 4.4 Compressore Efficiency vs Flowrate (Actual Operating Point) 25

Figure 5.1 Behaviourof the two performance curves from Figure 4.1 and 4.2 27

Figure 5.2 Comparison of thetwoperformance curves from Figure 4.1 and4.2 28

Figure 5.3 Behaviour of graphs from Figure 4.3 & Figure4.4 30

vi

LIST OF TABLES

Table 4.1 List of Gas Properties 18

Table 4.2 List ofDesign Data DischargeProperties 19

Table 4.3 List of Operating Plant DataDischargeProperties 21

vn

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND OF STUDY

Gas compressors are widely used in mechanical related industries in compressing the air /

gas to increase the pressure of the Gas. Applications of compressed gas vary from

consumer products, such as the home refrigerator, to large complex petrochemical plant

installations. Mainly, there are two types of Compressor; Dynamic Compressor and

Positive-Displacement Compressor. A widely used gas compressor is the centrifugal

compressor, one of the dynamic compressors which exhibit a contrary behaviour to the

positive displacement-type compressors. For example, in a reciprocating compressor

(positive-displacement compressor) a quantity of gas is drawn into the cylinder and

trapped by the action of the valves and motion of a piston. As the piston moves in the

cylinder, compression is achieved by direct volume reduction. By comparison, centrifugal

compressor achieve compression by applying inertial forces to the gas (acceleration,

deceleration, turning) by means of rotating impellers at high speed (Figure 1.1), that

continuously impact andperform workon the gas during operation.

K^

inp! It

TIP OF THE

IMPELLER

High Velocity,Higher PressureGas Outlet

EYE OF THE

IMPELLER

Low Velocity,Low Pressure

Gas Inlet

Figure.1.1 : Basic principles of centrifugal compressor. (Dresser Rand, 2008)

Next, the impellers rotation is utilized with a rotor shaft compresses the gas where the

high speed gas will enter a diffuser passage (Figure 1.2) which will enter the low flow

path which increase significantly the gas pressure (Figure 1.3). Stationary components

form a flow path for the gas to flow from suction to discharge. Pressurized gas is

contained inside a casing during operation.

SHAFTStAt

-PIAFHRAsr?

Figure 1.2 : Compression of highvelocitygas through the diffuser. (DresserRand, 2008)

Centrifugal Stage

Return, Bend —j* /\>

Every centrifugal compressor is designed to operate at a preferred optimum speed point

relative to the impeller design. Impellers are designed to raise the gas pressure within

limits that ensure the gas will flow at a desired production rate from the suction [inlet] of

the compressor to the discharge of the compressor. This operating point is graphically

defined (Figure 1.4) along an operating curve and is referred to as "Design Point"

operation which sometimes are called as the Best Efficiency Point.

P

A*S

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Q - FLOW

Figure 1.4 : Compressor performance curve(DresserRand, 2008).

Although in reality, it is rarely for the centrifugal compressors to runconsistently on the

design point parameters, it should be run at the nearest point to the design point

parameter. Therefore, a consistent check up or test on the centrifugal compressor

performance should always be observed. Such test is called Compressor Performance

Test. The main reasons forconducting suchtestareto confirm aerodynamic performance

of the compressor and the guaranteed operating conditions are met. The overall picture of

the Centrifugal Compressor Assessment is shown in Figure 1.5 in thenext page.

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.2 PROBLEM STATEMENT

Gas Compressor performance assessment is crucial in ensuring the Gas Compressor is

working at the best efficiency point (BEP) or Desired Point. The Gas Compressor

performance is assessed by evaluating the thermodynamics efficiencyas well as the head

produced. The assessment is conducted using computer program which normally is

proprietary to the owner of the program making it inaccessible to any other parties and

thus not available in the market. Therefore, this project is commenced to develop a

Generic Gas Compressor performance assessment program that can be used for any

model of the Gas Compressor.

OBJECTIVES

The main objectives of this project are:

• Design the performance assessment program

• Evaluate Gas Compressor performance

• Validate the assessment result with the actual data.

SCOPE OF STUDY

The work to be carried out can be summarized as follows:

• Develop mathematical model to allow thermodynamic analysis of the Centrifugal

Compressor system

• Validate the mathematical model by using an actual set of plant data obtained

from any Gas Compressor vendor

• Apply the mathematical models into the computer program

• Develop a user-friendly computer program to assess centrifugal compressor

performance based on the mathematical models.

CHAPTER 2

LITERATURE REVIEW

LITERATURE REVIEW

After a certain time period of operation, the Gas Compressor performance will drop and

need to be improved. The user must try to obtain the same compressor performance as

designed by the compressors' vendor since it is the point where the Gas compressor will

work at the best efficiency point or desired point. The operation of a centrifugal

compressor units means keeping the performance within the operating limits for which

machines were specified in order to avoid any inefficiency in the plant and to obtain the

highest economic profit. The Gas Compressor performance is assessed generally by

evaluating the thermodynamics efficiency as well as the head produced. The parameters

that should be taken into consideration when running a thermodynamic test of the

centrifugal compressors are:

• Polytrophic Head

• Inlet Flow Rate

• Compressor Efficiency

In Appendix III, the author has compiled several mathematical models from other authors

whose works are related to this project After making a critical literature review, the

author has decided to use the following as the reference of this project:

1.5.1 Polytrophic Head

The Polytrophic Head is an expression used for dynamic compressors to denote

the foot-pounds of work required per pound of gas. It can be defined as the energy

accumulated in the fluid of the system and expressed in feet (ft).

Article refer to Scott Golden, Scott A. Fulton & Daryl W. Hanson (2002), the

compressor curve flow term is always based on the inlet conditions; consequently

inlet gas density, p influences volumetric flow, v. Flow rate, v is shown on the X-

axis and head, H on the Y-axis. For a fixed impeller speed (RPM), the curve

shows that for a known inlet flow rate v, a fixed head, H is developed. Centrifugal

compressor inlet flow rate, v increases as the head, H decreases. Gas plant

operating pressure and gas composition determine the value of head, H.

28,000

ft 26,00010LL.

q 24fooy

5 22,0*0E tO /E 20-000

2 18,000

16,000

2,800 3,000 3,200 3,400 3,600 3,800 4,000 4,200

VOLUMETRIC FLOW, ICFM

Figure 2.1 : Compressor performance curve. (Scott Golden, Scott A. Fulton and DarylW. Hanson, 2002)

Increasing suction pressure, Ps, decreasing gas plant operating pressure, PD

and/or decreasing process system pressure drop, Pdrop will increase inlet flow rate,

v as long as the compressor is not operating at choke flow. A compressor curve as

can be seen in Figure 2.1 starts at the surge point and ends at stonewall, or choke

flow. The surge point is the head at which inlet flow is at its minimum. At this

point, the compressor suffers from flow reversal, which is a very unstable

operation that is accompanied by vibration and possible damage. Surge begins

when the operating point of the compressor crosses the surge line. Surge line is

the stability limit of the compressorperformance map [7].

On the other end of the curve is the choke (or stonewall) point. At the choke

point, the inlet flow through the compressor cannot increase no matter what

operating changes are made. Therefore, the range of compressor performance is

defined between these two flow head limitations. Normally, the curve is flat near

the surge point and becomes steeper as flow is increased. Thus, small head, H

changes near the surge point causes a large increase in compressor flow rate

capacity, v. As compressor operation moves toward stonewall, decreasing head, H

has less influence on inlet flow rate because the curve slope increases. As the

stonewall point is approached, changes in head, H will have negligible effect on

inlet flowrate [3].

Equation 1 shows the polytrophic head term. (Appendix III-E)

Hpoly[M1,545

Z«JS*MW "'* ' U-ly

Where ;

Zavg is the average compressibility factor between the suction and discharge

Z +Zsection, Zavg =—- —;

Ts is the gas suction temperature (R);

Ps is the gas suction pressure (psia);

Pd is the gas discharge pressure (psia);

k is the ratio of specific heat k

MW is the gas molecular weight

v/C,

k-\

£*-l "(I)

The value of the constant 1545 in the Equation 1 represents the universal

gas constant, R which:

1545 [/£'%]R= ^ =lfUb/,MW [lb/mol]

9

°fi>]lb.mol.°R

The compressibility, Zs value is determine at the suction condition with

respect to the suction pressure, Ps and suction temperature, Ts. While for

the Zd the value is determine at the discharge condition.

The value of Z at each suction and discharge can be determined from the

following equation:

Pv = ZRT

where P is the absolute pressure in Pascal, Pa.

v is thespecific volume in m3/kg.

R is the Universal Gas Constant in J/kg.K

Tis the absolute temperature in Kelvin, K

Specific Heat Ratio, k is the ratio of the specific heat at constant pressure,

Cp to the specific heat at constant volume, cv. These two values can be

obtainedfrom the thermodynamic table(refer Appendix VI).

Reducing polytrophic head, Hwill increase compressor capacity, vbymoving the

operating point to the right (Figure 2.2). A higher gas molecular weight, MW

raising suction pressure, Ps or lowering discharge pressure, PD are few process

changes that move the operating point to right of the performance curve

(Figure 2.2). However, the gas temperature, T changes have little influence on

head, H.

10

28,000

m*• 27,000

X 26,000o

§2 24,000

23,000

1,500 FT HEAD

25,000

7,700 RPM

11,500 12,000 12,500 13,000 13,500 14,000 14,500

VOLUMETRIC FLOW, ICFM

Figure 2.2 : Any process changes will moves the operating point on the curve. (ScottGolden, Scott A. Fulton and Daryl W. Hanson, 2002)

Volumetric Inlet Flowrate

The Compressor performance curve is also developed based on the volumetric

flowrate capacity of the suction conditions. The volumetric flowrate capacity is

located at the x-axis of the compressor performance map. Typically, the unit of

ACFM (actual cubic feet per minute) is used to represents the volumetric flowrate

capacity. However, some compressor operators & manufacturers use ICFM (inlet

cubic feet per minute). But ICFM is not a standard gas flow metering units since

wet gas is a compressible fluid, and thus changes in a compressor suction

conditions that increase the gas density will reduce the wet gas volumetric flow

rate and free up compressor capacity. Hence, for a better result, the author has

decided to use the unit of ACFM to represent the flowrate capacity.

The equation for volumetric flowrate capacity is:

Where

14.73xQxZTACFM =

520xPsx0.00144

Z is the Compressibility Factor at the inlet

Ts is the Suction Temperature in (°R)

Ps is the Suction Pressure in (psia)

Q is the unit flow in MMcfd

11

...(2)

1.5.2 Compressor Efficiency, rjXam

Compressor efficiency can be measured using suction and discharge gas

temperatures. However, the gas temperature measurement necessary for accurate

compressor efficiency measurement requires "laboratory" type temperature

measurement accuracy that is not practical for field measurement The equation

for Compressor efficiencyusing gas temperatures is:

ozn _vlsJ°MTs + 460

Td~Tsx

A-l

-1 ... (3)

where Ts is the suction temperature Fahrenheit,°_F

Td is the discharge temperature in Fahrenheit,0^

the value 460 is to convert the Temperature into the unit of

Rankine, R.

Commonly, the efficiency of a compressor ranged from a minimum of 60% to a

maximum of 80 %. Lower than this value shows the operator that maintenance is

required.

12

CHAPTER 3

METHODOLOGY

.1 METHODOLOGY AND PROJECT WORK

3.1.1

CompileMathematical

Model

Decide the most appropriate model

Development ofProgram

Critical DesignReview

Figure 3.1 : Methodology of the entire project

13

Polytrophic Head

Flowrate Capacity

Compressor Efficiency

Manual Calculations

Basic SpreadsheetMicrosoft Excel

User Friendly,Modem-look

Matlab / Labview

3.1.2 Compilation of Mathematical Model:

In this part, the author would compile several mathematical models which are

related to a thermodynamic of a compressor system; i.e. Polytrophic head,

Volumetric Flowrate and also the Compressor Efficiency. These mathematical

models are taken from anyprevious author's paper-work, training manual, lecture

notes and etc which are related to the centrifugal systems. Each mathematical

model is similarfrom one author to another, but there are slight different in term

of the results output.

The author will then compare all the compiled mathematical models to choose

one which is the most suitable mathematical model for this project. The criteria of

the most suitable mathematical model are based on the compromise between

accurate result and simplicity.

After the author has chosen a particular mathematical model for the project, the

next step would be using the mathematical model in a program to evaluate the

outputof the centrifugal gas compressor. In order to buildthis program, the author

would be usingeitherMatLab software or Labview software. However, before the

author uses the said software, the author would first develop the basic spreadsheet

by using Microsoft Excel.

14

3.1.3 Collection of Plant Data:

In order to evaluate these mathematical models (Appendix III), the author will use

a same data acquired from the plant as the input (refer Appendix V). The said

plant data must at least consist of:-

• Inlet Pressure

• Inlet Temperature

• Flowrate capacity

• Gas compositions, thus the Gas Molecular Weight

The data can be obtained from any plant/factory that operates centrifugal

compressor. The author however can obtain the set of data from PETRONAS

Fertilizer, Bintulu in Sarawak; the place where he has had gone through his

industrial internship. Example ofplant data can be seen in Appendix IV.

However, the example of plant data showed in Appendix IV is a Design

Characteristics of a particular Centrifugal Compressor. Thus, it is not an actual

data of the centrifugal compressor. The user will have to use this data as the

Design Point / Recommended Point / Best Efficiency Point for the Centrifugal

Compressor. And next, the user should have another list of actual data for the

same centrifugal compressor from the operator. He should then compared the

current performance of the centrifugal compressor (evaluated from the actual

data) with the designpoint (refer. Appendix IV). The illustrationof the centrifugal

compressor performance assessment can be seen above in Figure 1.5.

However, the author will use these set of data obtained to demonstrate the

performance assessment of the centrifugal gas compressor. Using the same

flowrate from the Design Data, the operator has come out with the Actual

Operating Data. The compilation of these data can be seen in Table 4.2 and

Table 4.3.

15

3.1.4 Development of Computer Program

The last stage of this project would be the development of computer program to

assess centrifugal compressor performance. The computer program would be able

to plot the centrifugal compressor performance map after the user has entered

input to it.

As a start, the author would use Microsoft Excel to construct a basic spreadsheet

in order for him to have a rough idea on the computer program but still meets the

main objective. At this level, the user would have to enter the particular properties

of the gas being compressed in the centrifugal compressor in order to obtain a

particular output. The properties of the gas are:

• Gas Compositions (Molecular Weight or Percentage)

• Inlet Pressure & Temperature

Next, the user would need to vary the flowrate capacity and as well as discharge

pressure. Each vary would determine one specific point for the compressor

performance map (Appendix IV). Basically, the detailed processes in the

development of the basic spreadsheet are:

i. Construct a column for input to be entered

ii. Set any unknown parameters using assumptions

iii. Evaluate polytrophic head and Flowrate Capacity for the first point of the

Compressor Performance Map

iv. Evaluate polytrophic head and Flowrate Capacity for the second —final

point

v. Plot the graph

vi. Repeat the process for other data in order to make comparison

16

However, the author does not intend to use basic spreadsheet as the main tool to

assess the centrifugal compressor performance assessment since they are few set

backs using it. They are:

the instructions may be unclear for a first time user,

the user has to manually plot the performance curve by selecting the

correct data,

the user has to save each performance curve construct —thus he can then

compare the current compressor performance with the one recommended

by the manufacturer

Therefore, after developing the basic spreadsheet, the author would then start to

use more advancedsoftware such as Matlab or LabView to develop the computer

program that able to assess the centrifugal compressor performance. In the end,

the computer program will be a user-friendly, easy to conduct, and modem-look.

17

CHAPTER 4

RESULTS

4.1 THE PLANT DATA

For demonstration purposes, the author will utilize the developed program

to evaluate the performance of the centrifugal compressor based on the obtained

plant data. For this purposes, the author will use the basic spreadsheet program

developed in order to have a quick grasp of evaluation on the main concept of the

program. The obtained plant data for both design point and actual operating point

can be seen in Appendix VII. For the ease of reference, Appendix VII has been

compressed into the table below:

Table 4.1 j__List_ofjrasJ^ropertie^orjDO^^ operating plant data.1 Properties j Unit T™ Value: Atm Pressure i barg j 1.01 "j

Suction Pressure, Ps barg [ 3.43 \Suction Temperature, Ts °C 20.00

SpecificVolume, v (from table) [ kJ/kg i 0.3083

1Specific Heat at Constant Volume, cv{from table) ' kj/kg 1.66

Specific Heat at Constant Pressure, cp (from table) ! kJ/kg \ 2.25

Gas Molecular Weight, MVV '• g/mol ~™ ™* l7.03Specific Heat Ratio, k ,' - [ 1.36

±^Z^ZZ7IlTrZlIl~" 1""" ^ZZZZlZZ.""'"^"™^??!Universal Gas Constant, R —j- ft ^^̂ ^^^ or * ^- ~ ^^Specific GasConstant, R ' J/kg.K " 488.20Compressibility Factor, Z ; 0.96

Table 4.2 List of design data discharge properties.

#

1

Flow Rate

q ift3/min)

Discharge „ .° Discharge Pressure

Temperature

Tdro ?*{bar9)Pressure Ratio

Pr

3450 100 4.73 1.29

2 3800 110 4.72 1.29

3 4200 120 4.69 1.28

4 4600 130 4.63 1.27

5 5000 140 4.55 1.25

6 5400 150 4.44 1.23

7 5800 160 4.28 1.19

8

9

6100 170 4.13 1.16

3690 100 4.95 1.34

10 3800 110 4.94 1.34

11 4200 120 4.93 1.34

12 4600 130 4.88 1.33

13 5000 140 4.82 1.31

14 5400 150 4.72 1.29

15 5800 160 4.61 1.26

16 6200 170 4.43 1.23

17 6490 180 4.24 1.18

18 3950 100 5.18 1.39

19 4200 110 5.16 1.39

20 4600 120 5.13 1.38

21 5000 130 5.07 1.37

22 5400 140 5.01 1.36

23 5800 150 4.91 1.33

24 6200 160 4.78 1.30

25 6600 170 4.58 1.26

26 6920 180 4.37 1.21

27 4200 100 5.44 1.45

28 4600 110 5.40 1.44

29 5000 120 5.36 1.43

30 5400 130 5.28 1.42

31 5800 140 5.21 1.40

32 6200 150 5.11 1.38

33 6600 160 4.96 1.34

34 7000 170 4.77 1.30

35 7400 180 4.54 1.25

Continue . . .

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#

1

Flow Rate

q {ft3/min)

Discharge _. ._ . Discharge PressureTemperature „ ,,

Tdro p*{barg)Pressure Ratio

Pr

3450 100 4.74 1.30

2 3800 110 4.74 1.29

3 4200 120 4.71 1.29

4 4600 130 4.65 1.28

5 5000 140 4.56 1.25

6 5400 150 4.46 1.23

7 . 5800 160 4.28 1.19

8

9

6100 170 4.15 1.16

3690 100 4.96 1.35

10 3800 110 4.96 1.34

11 4200 120 4.93 1.34

12 4600 130 4.89 1.33

13 5000 140 4.83 1.32

14 5400 150 4.74 1.29

15 5800 160 4.64 1.27

16 6200 170 4.46 1.23

17

18

6490 180 4.25 1.18

3950 100 5.22 1.40

19 4200 110 5.18 1.39

20 4600 120 5.17 1.39

21 5000 130 5.10 1.38

22 5400 140 5.02 1.36

23 5800 150 4.93 1.34

24 6200 160 4.79 1.31

25 6600 170 4.59 1.26

26

27

6920 180 4.38 1.21

4200 100 5.45 1.45

28 4600 110 5.41 1.45

29 5000 120 5.35 1.43

30 5400 130 5.30 1.42

31 5800 140 5.22 1.40

32 6200 150 5.12 1.38

33 6600 160 4.99 1.35

34 7000 170 4.81 1.31

35 7400 180 4.56 1.25

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I—'• g

4.2 THE PERFORMANCE CURVE

By using the data from Table 4.2 & Table 4.3, two separate Performance Curves

of Polytrophic Head at the Y-axis versus Flowrate at the X-axis are plotted. These

two curves are then compared to evaluate the performance of the compressor.

Refer to the figures (Figure 4.1 & Figure 4.2) below to see the differences: The

behavior of each figure is discussed on the next section.

Head (ft)

30000

25000

20000

15000

10000

5000

1000 2000 3000 4000 5000 6000 7000 8000 9000 lOQOd

Flowrate Capacity(ACFM)

Figure 4.1 : Performance curve of the design point

23

Head (ft)

30000 -—^^

H|^HHH3^^^flH^^HH^^^^

25000 Sj _..;..... 9,500 EPM __ __ _ _

': " ' 9,000 RPM ^^ ' ^%&^v•

20000 -/ 8,500 RPM ,., . ^%^ ^v \ ^,M

-----'.*X„^ '**^""""" Ik ~"~"* .„ ..„,

8,000 RPM ---_..„ "->:.>.. \^ X \ H

15000 \7,500 RPM ;-..._ '̂ s;.^

'V- 'fk v\ _. 1• »-—•. '"•:.•-. v-. vv• \". V-, H10000 -^^H • -' " :-;•:; ' -;r -l — 15000 ^^H ,......,

- ~ - -- - - ••« Io ^^H 1

0 2000 4000 6000

Flowrate Capacity(ACFM)

8000 10000

Figure 4.2 : Performance curve of the actual operation data.

4.3 COMPRESSOR EFFICIENCY VS FLOWRATE

Additionally, a graph of Compressor Efficiency versus Flowrate for each curve is

plotted. These graphs are shown in figure below (Figure 4.3 & Figure 4.4). This

graphs show the efficiency of the compressor at anyparticular flowrate capacity.

The behavior of eachcurve is discussed in the next chapter.

24

Compressor

Efficiency {%)70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

0 1000 2000 3000 4000 5000 6000 7000 8000 Fl°wrate Capacity(ACFM)

Figure 4.3 : Compressore efficiency vs flowrate (design point).

Compressor.

Efficiency (%)70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0 -!

o looo 2000 3000 400o 5000 6000 7000 8000 F'°wrate Capacity(ACFM)

Figure 4.4 : Compressor efficiency vs flowrate (actual operating point)

25

CHAPTER 5

DATA EVALUATION & DISCUSSION

5.1 DATA EVALUATION

5.1.1 The Performance Curve

The two performance curves in the previous chapter represent the data obtained

from the PETRONAS Fertilizer Bintulu, Sarawak as compiled in Appendix VII.

The two data; Design Point and Actual Operating Point are taken from the same

centrifugal compressor. By using the same values of the flowrate from the Design

Point, the operator had obtained the actual polytrophic head values for the

centrifugal compressor. Thesevalues are calledActualOperating Data. These two

data; Design Data and Actual Operation Data the performance curves are plotted

as in Figure 4.1 and Figure 4.2.

There are number of curves in each of the figure, which represents the speed of

the compressor was running. The lowest curve represents the lowest speed which

was running around 6500 RPM and the highest curve represents the highest

compressor speed which was around 10,000 RPM. The lowest curves for both

figures (Figure 4.1 and Figure 4.2) have only8 points andthese numbers ofpoints

increase as the compressor speed increase. For instance, the second, third and

fourth (from bottom) curves for eachdata have 9 points in each curve, and the rest

have 10 points. The first point in each curve is called the surge point (the point

where surge will occur), while the last point is called the choke point. The line

that connects all the surge point is called the surge line; while the lineconnecting

the choke point is called the choke line.

26

Overall, the two performance curves are showing a similar behavior, data ranged

but a very slight different for the top curves. Apparently, we can see a same

characteristic / behavior of the curves which are; a slope-down curve as shown in

figure below:

Head (ft)

nuwrdie

Figure 4.5 : The two performance curves from Figure 4.1 and Figure 4.2 showthe same behavior; a slope-out curve

Although these two performance curves are showing the same behavior, there are

little differences for the top curves behavior. To see them clearly, the author has

superimposed both of the performance curves together as can be seen in the figure

on the next page (Figure 4.6).

27

Head (ft)

30000

25000

Actual Operating Data

Design Data

4Q&Q: :$&&&•

Figure 4.6 : Comparison of the twoperformance curves from Figure 4.1 andFigure 4.2.Green curves are the Design Datawhile curves in Orange are the Actual Operating Data

As shown in Figure 4.6, there are slight differences between the green curves

(design data) and the orange curves (actual operating data). These differences are

not much noticeable for the middle curves where the speed of the centrifugal

compressor is around 8000 RPM or operating nearby the 100% of the compressor

speed. The differences are much clearer for the top curves and the bottom curves.

28

There are few variables and conditions that lead to such differences of these two

(2) data types. These differences are not desirable and considered as drop of

performance. The reasons that lead to the performance drop are may due to

mechanical failure such as fouling inside the compressor, leakage of the system,

high friction between the devices and etc.

Thus, if the operators intend to run the compressor at the high compressor speed,

some modifications should be made in order to obtaina high efficiency. They are

required either to increase the compressor speed at the same flowrate, or increase

the discharge pressure to obtain a higher Polytrophic Head and eliminate any

mechanical failures and etc.

5.1.2 Compressor Efficiency versus Flowrate

The other two graphs in the previous chapter represent the centrifugal compressor

efficiency for the Design Point and Actual Operating. From the Design Point

Flowrate values, the operators are able to obtain the readings for the Actual

Operating Point. The Compressor Efficiency basically is derived from the

Temperature Readings and Pressure Ratioof the centrifugal compressor as can be

seen in Equation 3 in page 12.

There are number of curves in each of the figure, which represents the speed of

the compressor. The lowest curve represents the lowest speed which is running

around 6500 RPM and the highest curve represents the highest compressor speed

which is around 10,000 RPM. The lowest curves for both figures (Figure 4.1 and

4.2) have only 8 points and these numbers of points increase as the compressor

speed increase, i.e. The second, third and fourth (from bottom) curves for each

data have 9 points in each curve, and the rest have 10points.

29

Taken as a whole, the two graphs are showing a similar behavior and data ranged.

Apparently, we can see a same characteristic / behavior of the curves which are; a

slope-down curve as shown in figure below:

Compressor

Efficiency

Flowrate Capacity[ACFM)

Figure 4.7 : Graphs from Figure 4.3 & 4.4 are showing the similar behaviorcurve which is a non-linear slope-in curve.

From those two (2) figures as well, we can conclude that as the flowrate increases

the compressor efficiency of the compressor drops. Another thing that can be seen

here is that as the compressor speed increases the compressorefficiency increases

for the same value of the flowrate.

30

CONCLUSION

By using the program designed by the author, it provides the basic necessary evaluation

of centrifugal compressor by showing the operator at which point or condition does the

problem occurs. The operator then can check for any failure that brings to the differences

of the performance curves evaluated from the program. The differences of the

performance curves are often referredas performance drop of the centrifugal compressor.

Next, the operator can perform any action to remedy the performance drop and assure the

centrifugal compressor is operating at the highest efficiency which is closely related to

the fuel consumption of the centrifugal compressor driver. Therefore, consistent check-up

of the centrinigal compressor should always be made in order to maintain a high-

efficiency of the centrifugal compressor performance. This is to avoid the increase of

fuel-consumption and thus affecting the profits made. Two data types are required to

make a performance check. The Design Point where usually obtained from the

compressor manufacturer and the Actual Operating Data where is obtained from the

operator of the centrifugal compressor. These two (2) types of data are then compared to

each other to see any bid dissimilarities between them. Any dissimilarity in the

Performance Curve of the Actual Operating Data to the PerformanceCurve of the Design

Data shows that the centrifugal gas compressor is not running at the desired point at the

particular compressor speed and flowrate capacity. The operator is then able to make' any

modification or changes to the centrifugal compressor which will relocate the point of

dissimilarities of the curve to the desired point as in the Design Data's performance

curve. The said spreadsheet program can be used by any company with the permission

and approval of the university.

31

RECOMMENDATIONS

In order to improve the program, several things should be made. The LabView software

has the capability to run a real-time assessment ofany device. By connecting the program

from a computer to the centrifugal gas compressor, the operator will be able to run the

assessment continuously for a quick detection of performance drop. This will surely

enhanced the assessment mode of the centrifugal gas compressor. The user can as well

perform real-time thermodynamic analysis on thecompressor by usingthis software.

This program however, requires the operators to have Microsoft Excel installed into their

computer in order to run it. Thus, the other improvement that can be made is using

Microsoft Visual Basic to create a similar program. This is because Microsoft Visual

Basic can create a standalone / independent program without any Microsoft products

installed on the user's computer. Thus it can be run by any computer which is used to

perform the assessment.

32

REFERENCES

1. Brown, Royce N, 1997, "Compressor Selection and Sizing," Butterworth-Heinemen,

the United States of America.

2. Scott Golden, Scott A. Fulton and Daryl W. Hanson, 2002, "Petroleum Technology

Quarterly", Process ConsultingSemices Inc., Houston, Texas.

3. Scott Golden, Scott A. Fulton and Daryl W. Hanson, 2002, "Understanding

Centrifugal Compressor Performance in a Connected Process System" Petroleum

Technology Quarterly, Process- Consulting Sendees Inc., Houston, Texas.

4. Rolls Royce, Technical Training, 2008, www.rolls-rovce.com .

5. Rick Brown & Kevin Rahman, Pasific Gas and Electric Corporation, Turbine /

Compressor PerformanceMonitoringSoftwareand Flow Capacity.

6. Dresser Rand: Compressor Training, 2008, www.dresser-rand.com, info(5),dresser-

rand.com.

7. Syuieb Ali, Centrifugal Compressor, Basic and Understanding, 2006, PETRONAS

Carigali Sdn Bhd (PCSB)

8. Ing. Jiff Oldfich, CSc, 2004, Variable Composition Gas Centrifugal Compressor

Antisurge Protection, Klecakova Praha, Czech Republic

33

APPENDICES

I. Anatomy of Centrifugal Compressor (RollsRoyce Training, 2008)

II. Operating at Design Point (Dresser Rand Training, 2008)

Surge Point

P

A*S

S

u

R

E

(HEAD)

Ordinate

Abscissa'

Design Point

n—>

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Compressor Operating Curve Map

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XV

11

VI. a. Properties of various common gases:

THERMODYNAMICS

Molar mass, gas constant, and eritjcai-point properties

Molar mass,G3S

constant,

Critical-point properties

Tempera Pressure, Volume,Substance Formula A?kg/kmot 8 hi/kg • K* ture, K MPa m3/kfno!

Air 28.97 0.2870 132.5 3.77 0.0883Ammonia NH3 17,03 ' 0.4882 4C5.5 11,28 0.0724Argon Ar 39,948 0.2081 151 4.86 0.0749Benzene CSHE 78.115 0.1064 562 4.92 0 2603Bromine 3rz 159.808 0.0520 584 10.34 0 Ub5o-Butane C^Hjc 58.124 0.1430 425.2 3.80 0 2547Carbon dioxide C0Z 44.01 0.1889 304.2 7.39 0 0943Carbon monoxide CO 28.011 0.2968 333 3.50 0 0930

Carbon tetrachloride ccs4 153.82 0.05405 556.4 4.56 0 2/o9Chlorine Cfe 70.906 0.1173 417 7,71 0 1242Chloroform CHCi3 119.38 0.06964 536.6 5.47 0 2403DichEorodifiuoromethane (R-12) CC!2F? 120.91 0.06876 384.7 4.01 0 21 —Dichlorofluoromethane {R-2.1) CHCfeF ' 102.92 0.08078 451.7 5.17 013Ethane• C^He 30.070 0.2765 305.5 4.48 0 14

Ethyl alcorsol CsHaOH 46.07 0.1805 516 6.38 oibEthylene C^Hj 28.054 0.2964 282.4 5.12 0 12

Helium He 4.003 2.0769 5.3 0.23 0 05

/r-Hexane CgHis 86.179 . 0.09647 507.9 3.03 0 36Hydrogen (normal) H? 2.016 4.1240 33-3 1.30 OOfcKrypton .Kr 83.80 0.09921 209.4 5.50 0 09

Methane CH„ 16.043 0.5182 191.1 4.64 009

Methyl atcohoi CH30H 32.042 0.2595 513.2 7.95 onMethyl chloride CH3C! 50.488 0.1647 436.3 • 6.68 0 14Neon m 20.183 0.4119 44.5 2,73 0 94

nitrogen Na 28.013 0.2968 126.2 3.39

Nitrous oxide N20 44.013 0.1889 309.7 7.27

Oxygen 0; 31,999 0.2598 154.8 5.08

Propane CaH8 44.097 0.1885 370 4.26 ^Propylene CaHfi 42.081 0.1976 36S 4 62

Sulfur dioxide SOf 64.053 0.1298 430.7 7 88

Tetrailuoroethane (R-134a) CF3CHaF 102.03 0.08149 374.3 4 067

TrrchlorafSuoromethartE (R-lll CCI3F 137.37 0.06052 471.2 4 38 ^

Water H20 18,015 0.4615 •" 647.3 22 09ml

Xenon Xe 131.30 0.06332 289.8 5 88 «•

'Theunit KJ/kg • KissqL*a!eat tokPs-B^k§-K.Tlw smconstatiscafculalsd from R== RJM, where J?s = &314 Niftnwl.- Kanrf W-stfie-Seurc&K. A, Kobe and R. £.l^m.Jc. Chemical Review52.ll9S3)l pp. T17--236;a*dASHRA£, Handbook ofFufstamenitfetfaatfa G# ^Society ofHeating, Refrigerating ano Air-Ccndifioning Engjneen;, Inc.,1933).pp. 16.4and36.1.

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